1. Field of the Invention
The present invention relates to a printer and, more particularly, to an apparatus of a label printer for detecting a termination of a web of printing medium that is continuously fed from a supply reel and severed into a label unit.
2. Description of the Related Art
Generally, a label printer, also called a mini-printer, prints out indicia on a sheet of printing medium such as stickers, receipts, etc., which are severed from a continuous web of printing medium reeled around a cylindrical core. For example, label printers are used in cash registers, or to print out numbers for customers waiting in line at a bank, etc. Such label printers employ detecting devices for detecting a termination of the printing medium.
FIGS. 1A and 1B show one example of a device for detecting the termination of the printing medium of the conventional printer, which is disclosed in detail in U.S. Pat. No. 5,884,861.
Referring to FIGS. 1A and 1B, the detecting device includes a frame 10 to which a web of printing medium reeled around a cylindrical core 2 is mounted for being fed by a predetermined unit label, and a level member 20 mounted on a side of the frame 10 to be pivoted towards and away from the frame 10.
The lever member 20 includes a first detecting protrusion 21 and a second detecting protrusion 22 protruding toward the frame 10, and a switch contacting protrusion 23 protruding oppositely from the first and the second detecting protrusions 21 and 22. The first and the second detecting protrusions 21 and 22 and the switch contacting protrusion 23 are vertically spaced from each other at a predetermined distance.
The first and the second detecting protrusions 21 and 22 enter or exit to or from the frame 10 through an opening (not shown) formed on the frame 10. Here, the reference numeral 30 refers to a limit switch for outputting a predetermined signal to a main controller (not shown) by a complementary operation with the switch contacting protrusion 23 during the pivoting movement of the lever member 20.
Meanwhile, the frame 10 has a guiding portion (not shown) that is stepped on an inner surface of the frame 10, for guiding the web of printing medium 1 therealong as the printing medium is near its termination.
That is, in an initial state, since the web of printing medium 1 is large in diameter, the first detecting protrusion 21 of the lever member 20 is interrupted by one end of the web of the printing medium 1 (see FIG. 1A), thereby restricting the pivoting movement of the lever member 20. As the switch contacting protrusion 23 presses the limit switch 30, a signal indicating an off-state of the limit switch 30 is output to the main controller (not shown) which thereby recognizes a normal state of the printing medium 1, and maintains normal operation of the printer.
Then as the printing medium 1 is continuously supplied and thus near its termination, the diameter of the web of the printing medium 1 is decreased to the state shown in FIG. 1B. In this state, the web of the printing medium 1 descends to a lower portion of the frame 10, and, accordingly, the first detecting protrusion 21 is released from interruption by the web of printing medium 1.
Simultaneously, as the second detecting protrusion 22 is inserted in a hollow portion of the cylindrical core 2, the lever member 20 is freely pivoted closer to the frame 10. In this position, the switch contacting protrusion 23 of the lever member 20 operates the limit switch 30 and generates an electric signal. Accordingly, a near-termination or termination of the printing medium 1 can be detected.
However, since the detecting device for detecting termination of the printing medium 1 of the conventional printer essentially requires a hollow hole in the core 2 that is reeled with the printing medium 1, the detecting device can only be used for a limited number of applications.
Also, when using the web of printing medium 1 which has a core 2 of different length, in order to connect the first and the second detecting protrusions 21 and 22 to the side of the printing medium, a user has to unscrew a screw (not shown) that fastens the frame 10 and the lever member 20, adjust the positions of the first and the second detecting protrusions 21 and 22, as necessitated by the particular core 2 being used, and refasten the screw to re-secure the frame 10 and the lever member 20.
Further, when using the web of printing medium 1 of different diameter, the contacting area of the first and the second detecting protrusions 21 and 22 changes. Consequently, the gap between the first and the second detecting protrusions 21 and 22 must be adjusted, or, alternatively, the lever member 20 must be replaced by a new lever member 20 having the necessary gap between the first and the second detecting protrusions 21 and 22. As a result, the user experiences inconvenience when working with this printer. Further, the accuracy in detecting a near-termination or termination of the printing medium 1 is deteriorated due to frequent adjustments described above.
For the foregoing reasons, when using the conventional detecting device of the printer for detecting termination of the printing medium, it is preferred that printing mediums 1 of different sizes not be used. Rather, it is preferred that limitations be placed on any variation in the size of the printing medium 1 used. Further, the frame 10 of the conventional printer has a shortcoming. It can only be used in a certain fixed posture.
The present invention has been made to overcome the above-mentioned problems of the related art, and, accordingly, it is an object of the present invention to provide a non-contact detecting device for detecting termination of printing medium in a printer, the device enabling a user to easily adjust an initial set position of a detecting portion to correspond to respective sizes of webs of the printing medium used in the printer.
Another object of the present invention is to provide a detecting device of a printer for detecting a termination of the printing medium having improved detection accuracy, user convenience, and compatibility, which can be variably used in a desktop posture or wall mount posture without having to adjust an initially set posture.
The above objects are accomplished by an apparatus of a printer for detecting a termination of a printing medium in accordance with the present invention, including a frame housing and supporting a roll of the printing medium for allowing supply of the printing medium by a label unit; printing medium detecting means for non-contact detecting of the termination of the printing medium according to varying diameter of the roll of the printing medium; and position adjusting means for adjusting an initial set position of the printing medium detecting means according to an initial diameter of the roll of the printing medium.
Another object of the present invention is accomplished by an apparatus of a printer for detecting a termination of a printing medium in accordance with the present invention, including a frame housing and supporting a roll of the printing medium for allowing supply of the printing medium by a label unit, the frame capable of being set on a first position and a second position; first printing medium detecting means and second printing medium detecting means for non-contact detecting of the termination of the printing medium according to varying diameter of the roll of the printing medium when the frame is on the first position and the second position; and position adjusting means for adjusting an initial set position of the first and the second printing medium detecting means according to an initial diameter of the roll of the printing medium.
According to one aspect of the present invention, the printing medium detecting means includes a window formed on the frame, capable of permitting a light to pass therethrough; a photo sensor module for emitting the light to the window, detecting light reflected from the window, and outputting the result in the form of an electrical signal; and a housing movably mounted on the frame for supporting the photo sensor module.
The housings have an aperture through which the light from the photo sensor modules is passed in a uniform width.
The aperture has a width in the range from 30% to 50% of the diameter of a light spot emitted from the photo sensor modules, and it is preferable that the housings have a shutter member slidably mounted on the aperture for adjusting the width of the aperture.
The position adjusting means includes a cam pin formed on the housing and a rotary knob rotatably mounted on the frame and having a cam groove for linearly reciprocating the housing in cooperation with the cam pin which is locked in the cam groove and moved along the cam groove in a cam fashion.
According to another aspect of the present invention, there is further provided a positioning device to the frame and the rotary knob for locking and unlocking a rotational movement of the rotary knob by a predetermined amount, and determining a moved location of the housing.
The positioning device in accordance with one preferred embodiment of the present invention includes a tab protrusion formed on an elastic rib which is movably formed on the rotary knob; and a plurality of tab grooves formed on the frame in a predetermined pattern, to which the tab protrusion is selectively seated according to the rotational movement of the rotary knob.
According to another aspect of the present invention, the frame has a guiding portion, stepped on an inner surface of the frame, for guiding the roll of the printing medium therealong to a lower portion of the frame as the diameter of the printing medium is decreased below a point at which the printing medium is nearly terminated.